POS0345 ASSESSMENT OF THE EFFECT OF TOFACITINIB ON BONE MARROW ADIPOCYTES AND BONE-FORMING OSTEOBLASTS UNDER NON-INFLAMMATORY AND INFLAMMATORY CONDITIONS
Authors: J. G. Letarouilly, J. Paccou, S. Badr, R. M. Flipo, C. Chauveau, B. Cortet, O. Broux, A. Clabaut
Journal: Annals of the Rheumatic Diseases (2022)

Background Systemic inflammation is the main factor underlying secondary osteoporosis in patients with rheumatoid arthritis (RA). The JAK inhibitors, such as Tofacitinib (Tofa), can control systemic inflammation and have beneficial effects on bone in various models. This might be due to direct effects on the bone microenvironment and not exclusively based on their anti-inflammatory function. Bone marrow adipocytes (BMAds) are abundant in the bone microenvironment. The effect of JAK inhibitors on BMAds is unknown, but evidence suggests that there is competition between human bone marrow-derived stromal cell (hBMSCs) differentiation routes toward BMAds and osteoblasts (Ob) in osteoporosis. Objectives To determine in various models whether Tofa influences directly bone marrow cell committment toward adipogenesis and osteoblastogenesis. Then, in a prospective pilot study, to investigate the potential effects of Tofa on bone marrow adiposity in patients with RA. Methods To study the effect of Tofa on cellular commitment, hBMSCs were cultured for 3 days in appropriate Ob- and BMAd- differentiation media (Ob-3d and BMAd-3d), together with Tofa at 200, 400 (equivalent to a therapeutic dose of 5 mg twice a day in RA patients) or 800 nM. To mimic inflammatory conditions, TNFα was added to the media at a dose of 1 ng/ml. This study was also conducted on mature BMAds and a similar treatment was applied for 6 days to mature BMAds at 14 days of differentiation (BMAd-20d). The impact of Tofa was determined by gene expression profile analysis, western-blot analysis and cell density monitoring. In parallel, in a pilot study of 9 RA patients treated with Tofa 5 mg twice a day (TOFAT study: NCT04175886 ), proton density fat fraction (PDFF) was measured by MRI (Dixon technique) at the lumbar spine at the start of treatment and at 6 months. Results In non-inflammatory conditions, the gene expression of Runx2 decreased in Ob-3d treated with Tofa 400 and 800 nM(p&lt;0.05). Conversely, BMAd-3d treated with Tofa (at 200, 400 and 800 nM) exhibited a substantial increase in the gene expression of PPARγ2, C/EBPα and Perilipin 1 (a marker associated with lipid droplet formation) compared to controls (p&lt;0.05). The increase in the expression of Perilipin 1 was also confirmed at the protein level. In inflammatory conditions, BMAd-3d and Ob-3d markers decreased considerably (PPARy2 and RUNX2, respectively, p&lt;0.05), but the addition of Tofa did not change the expression profiles of Ob-3d compared to TNFα controls. On the contrary, the analysis of PPARy2 gene expression showed that Tofa limited the negative effect of TNFα on BMAd differentiation (p&lt;0.05). The positive effect of Tofa on mature adipocyte (BMAd-20d) under inflammatory conditions was also supported by an increase in the density of differentiated BMAds (p&lt;0.001). These findings were consolidated by an increase in PDFF at 6 months of treatment with Tofa in RA patients (+6.9%, p&lt;0.01). Conclusion Overall, in vitro and clinical results suggest a stimulatory effect of Tofa on BMAds commitment and differentiation, which does not support a positive effect of Tofa on bone Disclosure of Interests Jean-Guillaume Letarouilly Consultant of: Sêmeia, Grant/research support from: Pfizer, Julien Paccou: None declared, Sammy Badr: None declared, René-Marc Flipo Consultant of: member of the advisory board Pfizer, Christophe Chauveau: None declared, Bernard Cortet: None declared, Odile Broux: None declared, Aline Clabaut: None declared